This invention relates to a biocide polymer material designed to inhibit the growth of micro-organisms in an aqueous solution, a device comprising said material, and a method to prepare said material-This invention also relates to a method to inhibit the growth of micro-organisms using said material.
When systems involving water, aqueous dispersions or aqueous solutions are used, growth of micro-organisms occurs with time, adversely affecting such systems.
This problem is particularly acute in the domain of photography. Conventionally, a photographic process includes several processing baths, which are aqueous solutions of photographically active substances. The photographic products are processed by successive immersion in these different solutions. During the processing, fragments of gelatin from the photographic material being processed accumulate in the processing baths, favoring the growth of micro-organisms.
Such growth, if it is not controlled, causes the formation of biofilms in the processing baths. These biofilms clog flows and significantly reduce the activity of the processing baths, thereby impairing the quality of the photographic images obtained.
To avoid such problems arising from the growth of micro-organisms, biocides are conventionally added to processing baths. These biocides are generally used in excess of the quantity necessary to inhibit the growth of micro-organisms. These biocides can be costly and toxic. In particular, the disposal of such compounds in the drains causes problems in waste water treatment plants that use the action of micro-organisms to treat sewage.
The quantity of biocide used can be reduced by various means. For example, patent application GB 2 223 662 describes an organic biocide chemically attached to a polymer by a bond that is cleaved by hydrolysis. The polymer is progressively hydrolysed, releasing the biocide in a controlled manner. However, this release of biocide does not depend on the presence of micro-organisms in the medium.
Patent application EP 733303 describes a biocide material comprising an organic biocide immobilized on a polymer support that is insoluble in water. The biocide is attached to the polymer by hydrolytically stable bonds.
Patent application EP 733304 describes a biocide material comprising a biocide of which the Log P value is at least 1.5, in which the biocide is immobilized on a support the surface of which is hydrophobic, by a mechanism of hydrophobic exclusion, P being the partition coefficent between n-octanol and water.
In such materials, the biocide is used xe2x80x9cas requiredxe2x80x9d whenever micro-organisms are present in the solution to be treated.
It is desirable to have a biocide material comprising a biocide consumed xe2x80x9cas requiredxe2x80x9d solely in the presence of micro-organisms, having a high inhibiting efficiency.
The invention relates to a biocide material comprising a water insoluble polymer support having immobilized thereon a biocide wherein the biocide material contains a water content from 30 to 60% based on the material weight.
The invention also relates to a method of preparation of said material, which comprises the following steps:
(i) Solubilizing a biocide in an organic solvent,
(ii) Contacting the biocide solution with a water-saturated water-insoluble polymer support in conditions such that the biocide is immobilized on the polymer support,
(iii) Removing the organic solvent,
(iv) Partially removing the water contained in the polymer support having immobilized thereon biocide to obtain a water content between 30 and 60% by weight.
Lastly, the invention relates to a method to inhibit the growth of micro-organisms in an aqueous solution, by contacting the aqueous solution with the biocide material of the invention, and a device to implement this method.
Biocides are compounds able to kill micro-organisms or inhibit the multiplication of micro-organisms such as bacteria, yeast, algae, molds, and lichens. Such compounds are known to the art. Examples of biocides are described in xe2x80x9cMicrobiocides for the protection of materialsxe2x80x9d, by W. Paulus, published by Chapman Hall, 1993.
Such biocides include sulfur- or nitrogen-containing heterocycles, compounds comprising active halogen groups, and quaternary ammonium salts.
In one embodiment of this invention, the biocides are isothiazolinones.
The isothiazolinones useful in this invention can be represented by the formula: 
wherein R represents a hydrogen atom, an alkyl group, an aryl group, an alkylaryl group, or an arylalkyl group, and R1 and R2 each independently represent a hydrogen atom, a halogen, an alkyl group, or R1 and R2 jointly represent the atoms necessary to form a condensed carbocycle, preferably comprising 5 or 6 members, for example a benzene ring.
Preferred biocides can be represented by the following formulae (I) or (II) 
wherein R3 is an alkyl group comprising 4 to 20 carbon atoms or an aryl group comprising 6 to 20 carbon atoms, 
wherein R5 is and R6 are selected from a hydrogen atom or a halogen atom, and R4 is an alkyl group comprising 1 to 20 carbon atoms.
Such biocides include for example Proxel(copyright) and Promexal(copyright) marketed by Zeneca, and Kathon(copyright) marketed by Rohm and Haas.
The polymer support useful in the scope of the invention is any support, insoluble in water and on which a biocide can be immobilized.
Useful polymers are for example the polymers obtained by condensation, such as polyesters, polyamides, polyurethanes, polyethers, epoxy resins, amino resins, phenol-aldehyde resins and acrylic polymers, and polymers derived from ethylenically unsatured monomers such as polyolefins; polystyrene, polyvinyl chloride, polyvinyl acetate, etc.
The polymer support may have any of various shapes, for example sheets, beads, fibers, etc. It may be porous or non-porous.
The support is usually inert towards the solutions to be treated. However, it can also be a resin that allows the composition of the solution to be treated to be modified in a controlled way, for example an ion exchange resin.
In the method of preparation of the invention, the biocide is dissolved in an organic solvent. For this purpose one or more biocides is dissolved in one organic solvent or in a mixture of organic solvents. The organic solvent or solvents usefil in the scope of the invention are for example heptane, hexane, dichloromethane, ethyl acetate, tetrahydrofiran or toluene.
Depending on the nature of the biocide, support or solution to be treated, the solution concentration can vary largely. However, the concentration of biocide in the organic solvent or solvents is usually at least 0.2 mol/l, preferably between 0.2 mol/l and 1 mol/l, and preferably between 0.25 mol/l and 0.50 mol/l.
The biocide material is formed by contact between the biocide solution and the water-saturated polymer support in conditions such that the biocide is immobilized on the polymer support.
There are numerous ways to immobilize the biocide on the polymer support.
According to the selected immobilization method, those skilled in the art are able to define the chemical steps required.
In a preferred embodiment, the biocide is immobilized by a mechanism of hydrophobic exclusion. In this case, the biocide must have a log P value of at least 1.5, P being the partition coefficient between n-octanol and water defined by
P=[biocide]octanol/[biocide]water
The value of Log P is well known in the literature concerning biocides. The values given hereafter are calculated by the method of V. Vishwanadan, A. Ghose, G. Revankar and R. Robins in xe2x80x9cJ. Chem. Inf Comput. Sci.xe2x80x9d, 1989, 29, 163.
In this type of mechanism of immobilization, when the biocide has a value of Log P less than 1.5, it can detach itself from the polymer support and contaminate the aqueous medium even when no micro-organisms are present. In this case, the advantage of the invention is not obtained, because the biocide is not released xe2x80x9cas requiredxe2x80x9d.
Supports particularly suitable to immobilize the biocide by hydrophobic exclusion are supports with hydrophobic surfaces, for example cross-linked polystyrene beads, preferably porous. Such beads are marketed under the names Amberlite XAD-4(copyright) and Amberlite XAD-2(copyright). In another embodiment, the support is a polyacrylic resin, for example Amberlite XAD-7(copyright).
When the immobilization of the biocide on the support is carried out by hydrophobic exclusion, the biocide material can be obtained merely by contacting the biocide solution with the water-saturated polymer support for a sufficient time to immobilize the biocide on the support. The contacting can be speeded up with stirring. The duration of contact between the polymer support and the biocide can range widely according to the support and the biocide selected. The optimum contact duration can be easily determined by those skilled in the art according to the substances present.
In an embodiment of the invention, the water and the solvent are eliminated by distillation.
Preferably, the water content of the biocide material is between 35 and 40% by weight of the material.
According to the shape of the polymer support, a biocide material in the form of sheets, particles, fibers, etc., can be obtained.
The biocide material of the invention, when it is contacted with an aqueous solution in which micro-organisms may grow, inhibits the growth of any such micro-organisms.
The contact between the biocide material and the solution to be treated can be effected in any of various known ways. For example, the biocide material of the invention or the device that makes use of such a material can be placed in a circuit in which the solutions to be treated flow, in order to optimize the contact between the micro-organisms and the biocide. The device can, for example, use the biocide material in the form of particles placed in a container through which the aqueous solution to be treated flows. The solution to be treated can also flow over strips of the biocide material. When the biocide material is porous, the solution to be treated can be allowed to percolate through the biocide material.
The material of the invention is especially well-suited to the treatment of photographic solutions for processing and washing photographic elements.